The disclosure relates to an electrically controlled pressure control valve for an adjustable hydrostatic pump and to a hydrostatic pump therewith.
The adjustment of the delivery volume of hydrostatic pumps can be accomplished with an adjusting pressure medium, with which an adjusting cylinder of a pivoted cradle of an axial piston pump can be supplied and filled, for example. In this case, a control valve controls the connection of an adjusting pressure medium source to the adjusting cylinder.
As feedback of the (achieved) adjustment to this control valve, there is a known practice in the prior art, following a first principle, of providing travel or force feedback from the adjusting device (e.g. the adjusting cylinder) to the control valve. As a result, the control valve is influenced in such a way with increasing adjustment and thus an increasing delivery volume of the pump that the adjusting pressure medium is throttled and the adjustment is reduced or stopped.
Publications DE 100 01 826 C1 and DE 199 49 169 C2 show control valves of this kind which are each designed as cartridges and the respective longitudinal axes of which coincide with the longitudinal axis of an adjusting piston of the adjusting cylinder. In this case, feedback of the travel of the adjusting piston, which is converted into a force by an interposed spring, is implemented.
In the case of pressure control valves for adjustable hydrostatic pumps, there is a known practice in the prior art, following a second principle, of connecting the pressure control valve to the high pressure side of the pump to be controlled in order to detect the working pressure thereof and feed it back to the pressure control valve. In this case, the working pressure acts on the valve body of the pressure control valve in the direction of a reduction in the delivery volume and hence in the pressure of the pump (feedback of the working pressure of the pump).
The adjusting pressure medium which is necessary to supply the adjusting device of the pump can furthermore be tapped from the working line of the pump and throttled by means of the pressure control valve in accordance with the desired adjustment of the pump and fed to the adjusting cylinder.
The publication by the applicant, RD 9 2711/01.12 A10VSO, shows a pressure control valve of this kind with feedback of the working pressure to the pump to be controlled on page 11/48. The pressure control valve acts as a pressure limiter for the working pressure of the pump. For this purpose, a spring acts on the valve body of the pressure control valve in the direction of an increase in the delivery volume of the pump. The maximum pump working pressure to be established can be set by setting the preloading of the spring.
On page 15/48, the same publication by the applicant shows a pressure control valve arrangement in which an electrically actuated pilot control valve is added to the main pressure control valve, by means of which pilot control valve it is possible to set a control pressure that acts together with the spring on the valve body of the main pressure control valve in the direction of an increase in the delivery volume of a pump. An electrically controlled pressure control valve arrangement is thereby created in which an increase in the current his electromagnet causes a pressure reduction in the control pressure and hence movement of the valve body of the main pressure control valve in the direction of a reduction in the delivery volume and hence a reduction in the working pressure of the pump. The electrically actuated pressure control valve arrangement thus has a negative characteristic, which sets a maximum delivery volume of the pump in the event of a power failure at the electromagnet (fail safe).
The disadvantage with the last-mentioned electrically controlled pressure control valve arrangements is that the outlay in terms of equipment and the installation space requirement are high since this involves a combination of the main pressure control valve and of the additional electrically controlled pilot control valve.
Given this situation, it is the underlying object of the disclosure to provide an electrically controlled pressure control valve for hydrostatic pumps and a hydrostatic pump, the outlay for which in terms of equipment and the installation space requirement are reduced.